Class II Major Histocompatibility Complex (MHC) antigens are two chain heterodimers in which both the Alpha chain and the Beta chain are glycoproteins. They are normally expressed on the surface of peripheral B cells and macrophages in both mouse and man and their expression can also be induced in T cells. They function as 'restricting elements' for presentation of foreign antigens to T lymphocytes, i.e. they are the products of the immune response genes and determine whether or not a humoral immune response is generated to a particular foreign antigen. The general goal of this research is to study the biosynthesis of human Class II antigens on the surfaces of cells utilizing cloned genes (as well as mutated genes) transfected into a variety of cells, and to use these expressed proteins to investigate several important areas of molecular immunology involving these glycoproteins. In particular we wish to understand the molecular basis of 'restriction' of the immune response and some of the factors which control expression of these surface proteins. The specific aims are: 1) To introduce cloned Alpha and Beta chain genes of human Class II MHC antigens within a) cosmid vectors containing one or more genes, b) plasmid vectors (pBR322) containing a single gene and c) retrovirus vectors containing a single gene by transformation (a,b,c) or infection (c) of a variety of human, monkey and mouse cell lines. 2) To use this system to study specific Alpha/Beta chain combination and expressions (e.g.) DRAlpha with DRBeta) or heterospecific combinations of genes in different subfamilies (e.g. DRAlpha with SBBeta or DCBeta) as well as heterospecific combinations within a subfamily (e.g. DXAlpha with DCBeta). 3) To introduce mutations in the cloned genes which will result in expression of proteins with altered glycosylation sites or altered polypeptide sequences in order to probe the role of the glycan moiety and of specific regions of the polypeptide in chain association, cell surface expression and function. These experiments are intended in particular to probe factors which determine the range of immune responses. 4) Potentially to explore the role of the Gamma (invriant) chain in Class II antigen biosynthesis.